A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Is it ever legal to not install a MBJ in a CT cabinet? I looked at a 600A cabinet today and was told the MBJ was an option:?
Most of the CT cabinets in this area are bonded to the neutral. As I read 250.92(B) it is permissible.
I have always "split" the ground, bonded incoming conduit, nipple to disconnect and then continued on into first means of disconnect. I don't believe I have seen the Neutral terminated inside the CT can itself.
So you install a rigid nipple from the CT cabinet to the first disconnect, install a bond bushing to the nipple and land the GEC to the bond bushing and then to the neutral bar in the disconnect? Is that what you are referring to the "split" ground? Meter sockets bond the neutral to the case, why not CT cabinets?
Your post has me confused. Just exactly what are you calling an MBJ?Is it ever legal to not install a MBJ in a CT cabinet? I looked at a 600A cabinet today and was told the MBJ was an option:?
(B) Main Bonding Jumper. For a grounded system, an unspliced
main bonding jumper shall be used to connect the
equipment grounding conductor(s) and the service-disconnect
enclosure to the grounded conductor within the enclosure for
each service disconnect in accordance with 250.28.
Exception No. 1: Where more than one service disconnecting
means is located in an assembly listed for use as service
equipment, an unspliced main bonding jumper shall
bond the grounded conductor(s) to the assembly enclosure.
Exception No. 2: Impedance grounded neutral systems
shall be permitted to be connected as provided in 250.36
and 250.186.
Your post has me confused. Just exactly what are you calling an MBJ?
The MBJ(s) always gets installed in the service disconnect enclosure(s).
Okay... drop "main".OK....Maybe I have the terminology wrong, but I'm referring to a physical connection between the CT cabinet enclosure and the grounded conductor just like 200/320A meter sockets use.
Okay... drop "main".
250.80 requires the metal service enclosures and raceway be connected to the grounded system conductor (or grounding electrode conductor if an ungrounded system). Typically the direct, shortest jumper method is used. However, if metal raceway is used, doing so creates a parallel path for neutral current, thus the option to not directly bond [250.6]... and run a bonding jumper from the service disconnect enclosure... or use direct bonding and insert a non-conductive section of raceway (or fitting) between CT cabinet and service disconnect enclosure(s).
The thing is, it is a violation of 250.6. ... "The grounding of ... conductive normally non?current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable currents".Understood but in this case or that of any service, between the meter and the MDP, the parallel path is acceptable IMO, if a metallic raceway is used. PVC would be a better choice to eliminate that result but sometimes isn't spec'd.
The thing is, it is a violation of 250.6. ... "The grounding of ... conductive normally non?current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable currents".
Isolating the grounded neutral from the metal enclosure and raceway at the CT cabinet, and running a bonding jumper for the cabinet and raceways to the service disconnect eliminates the parallel path. IMO, this is a practicable method in all installations using metal enclosures and raceways.